Vaccines containing antigens from more than one pathogenic organism within a single dose are known as “multivalent” or “combination” vaccines. Various combination vaccines have been approved for human use in the EU and the USA, including trivalent vaccines for protecting against diphtheria, tetanus and pertussis (“DTP” vaccines) and trivalent vaccines for protecting against measles, mumps and rubella (“MMR” vaccines). Combination vaccines offer patients the advantage of receiving a reduced number of injections, which can lead to the clinical advantage of increased compliance (e.g. see chapter 29 of reference 1), particularly for pediatric vaccination.
Current combination vaccines can include relatively high amounts of aluminium salts as adjuvants which causes concern to some patient pressure groups despite empirical safety studies [2,3]. For instance, the aluminium levels in known combination vaccines are as follows (see also Table A below):
Trade nameAntigensAl+++ content per unit dosePediacelD-T-Pa-Hib-IPV0.33 mgPediarixD-T-Pa-HBV-IPV≤0.85 mg PentacelD-T-Pa-Hib-IPV0.33 mgTritanrix-HepBD-T-Pw-HBV0.63 mgQuinvaxemD-T-Pw-Hib-HBV 0.3 mgHexavacD-T-Pa-IPV-Hib-HBV 0.3 mgBoostrix (USA)D-T-Pa≤0.39 mg 
A vaccine with lower levels of aluminium would be helpful for some patient groups, and it is an object of the present invention to provide such vaccines, ideally without loss of vaccine potency. Another drawback with current vaccines is that they require relatively high amounts of antigen, whereas various documents show that protective effects might be achieved with lower amounts of antigen e.g. reference 4 shows that the amount of Hib antigen can be halved in a D-T-Pw-Hib vaccine without loss of immunological response, and reference 5 argues that a reduced WV dose can be used while maintaining an adequate level of protection against polio. It is an object of the present invention to provide further vaccines with reduced amounts of antigen, ideally without loss of immunoprotective effect.